DescriptionA cave-dwelling salamander. This is the only known blind, troglobitic salamander which undergoes a complete metamorphosis. Adults are white, pinkish white, or light brown on the dorsum and venter. The reduced eyes are dark spots visible through the partially fused eyelids. Adults are 36 - 70 mm snout to vent length (75 - 135 mm total length) with 16 - 19 costal grooves. Sexually mature males have a slightly swollen upper lip and a pair of cirri (papilla-like extensions from the upper lip). Like many other plethodontid salmanders, males also have a mental gland, a raised area on the chin used in courtship.
Hatchlings are 13 mm snout to vent length (17 mm total length). The larvae have bushy gills and a moderately high dorsal tail fin. Larvae are lightly pigmented (tan dorsally, often weakly stippled or mottled) and have functional eyes. The eyes become atrophied and the eyelids fuse at metamorphosis (Brandon 1970; 1971; Petranka 1998; Besharse and Brandon 2005).

Restricted to two plateaus in the Ozark region of southern Missouri, extreme southeastern Kansas, and adjacent areas in Arkansas and Oklahoma. Missouri distributions in 25 counties were mapped by Johnson (2000). Adults are not known outside of the twilight and dark zones of caves and sinkholes, but larvae are found in cave entrances and springs as well as nearby creeks. Adults may be found in water or on moist vertical rock walls which extend out of the water. Sandy or gravelly substrates are preferred by the larvae (Hendricks and Kezer 1958; Brandon 1970, 1971; Petranka 1998; Trauth et al. 2004).

Life History, Abundance, Activity, and Special BehaviorsCourtship has not been described. Mating occurs from late spring through summer. Oviposition likely occurs from late summer to fall when females disappear from the surface. Oviposition sites have not been documented, but presumably are in rocky crevices. Female attendance of eggs is likely. Clutch size from one female was 13 (Brandon 1971; Petranka 1998).

The larval period lasts from 1 - 3 years (Brandon 1971) or 2 - 6 years or longer depending on locality and conditions. Adults are known to live for at least 12 years in captivity, but their lifespan in the wild is unknown. If E. spelaea is comparable to cave fish and crayfish their lifespan may be considerably longer, 20 - 25 years, than terrestrial salamanders as a response to energy resource limitations (Fenolio et al. 2014, Fenolio, personal communication).

This species is unique in that it starts life as a fully sighted larva but then metamorphoses underground into a terrestrial adult that loses its pigment and becomes blind, with the eyelids eventually fusing (Brandon 1970; 1971; Petranka 1998; Besharse and Brandon 2005). However, it is likely that some light sensitivity remains in the eye structures because adults have photophobic behavior. There three main hypotheses explaining why the eye forms but then becomes vestigial and loses its color. The first is that there is a link between the genes that code for skin pigment and eye pigment. However, this would not explain the loss of the structure in the eye. The second hypothesis is that early development of the eye plays a role in skull development. This hypothesis is supported by the fact that many blind cavefish also have eyes early in development that are completely loss after the skull is formed. The third hypothesis is that the loss of the eye helps the species conserve energy (Fenolio personal, communication). The energy economy hypothesis for loss of eyes was reviewed by Jeremy Niven (2015), who argued that the cost of developing and maintaining eyes is substantial as illustrated by a positive correlation in eye and brain size in fish in comparisons of cave, intermediate/hybrid, and terrestrial fish, which indicates that when eyes are present a substantial portion of the brain is needed for visual processing, and oxygen consumption rates. Energy savings from loss of eyes could reduce the amount of time needed for foraging and allow energy to be re-invested in other physiological processes, including reproduction. This hypothesis is reasonable for E. spelaea considering the resource limitation it experiences. Lastly, hypotheses two and three are not mutually exclusive and may both be accurate explanations (Fenolio, personal communication).

Grotto salamanders are most active during spring and summer months when moisture levels in caves are high, food is abundant, and courtship is taking place. Adults feed on aquatic and terrestrial invertebrates, including flies, mosquito larvae and beetles. Adults may function as a top predator in some cave systems. Predators have not been reported although larvae are likely to be vulnerable to crayfish (Brandon 1971; Petranka 1998).

The grotto salamander is most abundant in caves that harbor high numbers of bats (Hendricks and Kezer 1958; Bonett and Chippindale 2004; Brandon 1971). From late April to October, and particularly during the summer, gray bats (Myotis grisescens) make use of caves as maternity roosts (Hendricks and Kezer 1958; Bonett and Chippindale 2004; Brandon 1971). Bats deposit feces (guano) within the cave, leading to an increase in invertebrates associated with the guano. Grotto salamander larvae eat isopods, fly larvae, and snails (Brandon 1971; Petranka 1998), but in a highly unusual move for animals that are normally thought of as strictly carnivorous, grotto salamander larvae also consume bat guano (Fenolio et al. 2006). Bat guano is a source of high nutrition in a resource-poor environment (the cave) since bats have short digestive tracts and fast digestion times and do not extract the full nutritive value of food items. Guano has been found to contain twice the protein content and about two-thirds the calories of an equivalent volume of Big Mac hamburger. Microbial biofilms on the guano may provide extra nutritive value. The nutritive value of guano was found to be higher in terms of protein content, caloric density, and essential mineral content than a potential prey item, cave-dwelling gammarid amphipods (Fenolio et al. 2006).

Trends and ThreatsCaves represent a fragile ecosystem vulnerable to disturbance and pollution. Long-term monitoring will be needed to determine population trends of these animals (Petranka 1998). This species occurs within several protected areas, but local threats include degradation of ground water quality and forest clear-cutting, which indirectly affects the salamander by changing bat populations (Hammerson 2004).

CommentsThe species authority is: Stejneger, L. (1892). ''Preliminary description of a new genus and species of blind cave salamander from North America.'' Proceedings of the United States National Museum, 15, 115-117.

Recent molecular studies have shown that it is a close relative of species of the genus Eurycea that occur nearby. It differs strikingly from these species in its larger size and cave-related features, but because it is phylogenetically nested within the Euryea multiplicata complex, Bonett and Chippindale placed it in Eurycea. Thus its name was change from Typhlotriton spelaeus to Eurycea spelaea (Bonett and Chippindale 2004).

In an alternative to Linnean classification, the name Typhlotriton could be retained as a clade name, for example in Phylocode. Because mitochondrial DNA sequence divergence within E. spelaea is relatively great, some of the populations might be recognized as distinct species (two additional species were described in the past but now included within E. spelaea; Bonett and Chippindale 2004).

Bonett, R., and Chippindale, P. T. (2004). ''Speciation, phylogeography, and evolution of life history and morphology in plethodontid salamanders of the Eurycea multiplicata complex.'' Molecular Ecology, 13(5).

Brandon, R. A. (1970). ''Typhlotriton and T. spelaeus.'' Catalogue of American Amphibians and Reptiles. American Society of Ichthyologists and Herpetologists, 84.1-84.2.